Solid fuel

ABSTRACT

[Object] To provide a solid fuel suitable for thermal power generation by making use of the residue left after beneficial seeds, grains or bulbs are collected. 
     [Solution] A solid fuel which comprises a composition containing 70 wt % or more, on dry basis, of dried  Arundo donax, Leucaena leucocephala, Saccharum officinarum, Manihot esculenta , straw, seaweed, seagrass or algae and which is hot compression molded.

FIELD OF THE INVENTION

The present invention relates to a solid fuel. More specifically, itrelates to a solid fuel making effective use of the residue left afterbeneficial seeds, grains or bulbs are collected from plants which arecultivated in relatively large quantities or grow in nature.

Much more specifically, it relates to a solid fuel which makes effectiveuse of the above residue obtained from specific plants, produces assmall an amount as possible of a harmful gas or residue aftercombustion, generates a large quantity of heat and leads to thesuppression of the production of carbonic dioxide, especially a solidfuel suitable for use as a fuel for thermal power generation.

DESCRIPTION OF THE PRIOR ART

The causes of global warming which is one of the global environmentalissues include an increasing amount of carbon dioxide existent in air.Various approaches to the suppression of the production of carbondioxide are being made on a global basis. As one of the approaches, theproduction of biofuels and use of them in automobiles and power boilersas alternatives to fossil fuels such as coal and gasoline are underway.However, use of foods such as corn which are used as raw materials ofthe biofuels is breaking down ecological balance and economical balanceand therefore it cannot be said that this is the best approach. Thus, itis necessary to take global environment into consideration while effectson clothing, food and housing whose balance is indispensable for humanlives are minimized. Since this is a very difficult problem to besolved, various studies are under way but the problem is not solved yet.Then, a solid fuel making use of plastics is used in power boilers as analternative to oil and coal but it cannot be said that its effect ofsuppressing the production of carbon dioxide is satisfactory.

SUMMARY OF THE INVENTION Problem to Be Solved by the Invention:

Then, the inventors of the present invention conducted intensive studiesto develop a solid fuel which makes use of the residue left afterbeneficial seeds, grains or bulbs are collected and plants growing innature all of which are produced in relatively large quantities and canbe used as a new energy source capable of suppressing the production ofcarbon dioxide. As a result, they found that certain kinds of plants orresidue thereof is solidified to be effectively used as a solid fuel.They also found that the residue can be used especially as a solid fuelfor power generation and as a new energy source.

That is, when the residue left after beneficial seeds, grains or bulbsare collected from specific plants is thermally compressed and moldedunder specific conditions, a hard molded product can be obtained withoutusing a large amount of a binder (for example, a plastic) or a formretaining agent (for example, a rubber or adhesive) intentionally andthat the obtained molded product has a sufficiently large calorificvalue as a solid fuel. Further, they found that, surprisingly, themolded product has sufficiently high hardness and toughness, that is,excellent form retention stability though it contains the residue as themain component. This form retention stability is one of extremelyvaluable characteristic properties as a solid fuel, especially a fuelfor thermal power generation. A solid fuel goes through repetitions ofsteps such as storage, transportation and unloading after production(molding) before use. During these steps, fragmentation occurs and whenfragmentation becomes marked, this product becomes unsuitable for use asan industrial solid fuel.

It was found that the fragmentation and disintegration of the solid fuelaccording to the present invention hardly occur in these steps aftermolding before use by users, whereby the solid fuel can retain its formfor a long time as an industrial fuel having a suitable molded size,especially a fuel for thermal power generation.

Means for Solving the Problem:

The present invention was made based on the above finding. According tothe present invention, there is provided a solid fuel which comprises acomposition containing 70 wt % or more, on dry basis, of dried Arundodonax, Leucaena leucocephala, Saccharum officinarum, Manihot esculenta,straw, seaweed, seagrass or algae and is hot compression molded.

According to a preferred aspect of the present invention, there isprovided the following solid fuel.

-   (1) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of dried Arundo donax, Leucaena leucocephala,    Saccharum officinarum, Manihot esculenta, straw, seaweed, seagrass    or algae.-   (2) The solid fuel wherein the composition contains 85 wt % or more,    on dry basis, of dried Arundo donax, Leucaena leucocephala,    Saccharum officinarum, Manihot esculenta, straw, seaweed, seagrass    or algae.-   (3) The solid fuel which is obtained by compression molding the    composition at a temperature of 80 to 150° C.-   (4) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of Arundo donax.-   (5) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of Leucaena leucocephala.-   (6) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of Saccharum officinarum.-   (7) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of Manihot esculenta.-   (8) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of straw.-   (9) The solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of seaweed.-   (10) A solid fuel wherein the composition contains 80 wt % or more,    on dry basis, of seagrass.-   (11) The solid fuel wherein the composition contains 80 wt % or    more, on dry basis, of algae.-   (12) The solid fuel having a calorific value of 15 to 30 Mj/kg.-   (13) The solid fuel having an average size of 15 to 3,500 cm³.-   (14) The solid fuel having an apparent specific gravity of 0.3 to    0.6 g/cm³.-   (15) The solid fuel having a fragmentation ratio of 5 wt % or less    in a form retention stability test.-   (16) The solid fuel which is used for power generation.-   (17) Use of the above solid fuel as a fuel for power generation.

EFFECT OF THE INVENTION

According to the present invention, there can be provided a solid fuelmolded product having excellent form retention stability by making useof the residue of a certain kind of a plant which is cultivated in largequantities and used as food or feed. Particularly, there can be provideda solid fuel molded product as a solid fuel substantially composed of aplant residue, especially a solid fuel for power generation. Therefore,the solid fuel of the present invention is substantially formed from aplant in nature, does not produce a harmful gas and leads to thesuppression of carbon dioxide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Dried Arundo donax, Leucaena leucocephala, Saccharum officinarum,Manihot esculenta, straw, seaweed, seagrass or algae is used as the mainraw material of the solid fuel of the present invention. It is a driedproduct of the residue (stalk or leaf) left after beneficial seeds,grains or bulbs are collected.

The dried product may be a product which is dried to some extent thoughit contains a small amount of water. The dried product can be used as itis or after it is cut.

The above plants are described hereinunder.

-   (a) Arundo donax is a gramineous herbaceous perennial which grow    near the coast of a warm place.

It is also known as “yoshitake” (or giant reed) . Although it isarundinaceous, it is much larger than a reed and grows up to 2 to 4 m,and its stalk is as thick as a bamboo. Its rhizome is short, crawlshorizontally and becomes bushy. Its leaves are wide and linear, andtheir ends extend thinly.

-   (b) Leucaena leucocephala is a mimosaceous dediduous shrub. The    amount of biomass produced by this plant per year is incommensurably    larger than those of other plants, and some Southeast Asian    developing countries into which this plant was imported in the past    likewise actively make use of biomass produced by this plant.-   (c) Saccharum officinarum is a gramineous plant which belongs to the    family Saccharum. The press cake of Saccharum officinarum is called    “bagasse”. The bagasse is industrially used as a raw material for    the production of pulp for paper making and furfural, wax (sugarcane    wax) can be extracted from the bagasse, and octacosanol is separated    from the bagasse. It may also be used as a raw material of a medium    for the cultivation of cloud ear mushrooms.-   (d) Manihot esculenta is a euphorbiaceous tropical shrub which    belongs to the family Evodiopanax innovans. Its tubercle is a raw    material of tapioca, and it is cultivated in the tropical zone in    the world. Its leaf is composed of 5 to 10 follicles and its stalk    rises vertically. Several tubercles are grown at the root of the    stalk like a gentle concentric circle. The tubercle has a thin shape    with sharp ends.-   (e) Straw is the dried stalk of a gramineous plant such as rice or    wheat. The straw now tends to be treated as a very precious thing.    According to recent studies, experiments on the production of    bioethanol are carried out.-   (f) Seaweed is a collective term for marine seaweed which is grossly    visible. This means marine “seaweed” and does not include seed    plants.-   (g) Seagrass is a seed plant which grows in the sea and marine    waterweed. It is homonymous with seaweed which is algae but this may    be pronounced as “umikusa” as it is hardly distinguished from    seaweed when it is pronounced as “kaisou”.-   (h) Algae refer to aquatic photosynthetic eukaryotes.

The solid fuel of the present invention comprises a composition whichshould contain 70 wt % or more, preferably 80 wt % or more, on drybasis, of a dried product of the above residue, or may containsubstantially 100 wt % of the dried product. However, the compositionmay contain another component derived from a natural product, forexample, a binder such as rubber or starch, in an amount of less than 30wt %, preferably less than 20 wt %, particularly preferably less than 15wt %.

Out of the above plants, Arundo donax, Leucaena leucocephala, Saccharumofficinarum, Manihot esculenta or straw is preferred, and Arundo donax,Leucaena leucocephala or Saccharum officinarum is particularlypreferred.

To mold the solid fuel of the present invention, the above composition(particularly a fragmented dried product) should be compression moldedat a temperature of 80 to 150° C., preferably 100 to 130° C. For thermalcompression, a single-screw or double-screw hot extruder may be used.

It is particularly desirable to use a double-screw extruder. Thecomposition compression extruded from the extruder is discharged from acircular nozzle and cut to a suitable length so as to obtain acylindrical molded product.

At this point, a solid fuel having a desired size can be obtained bysetting the diameter of the circular nozzle to 25 to 50 mm, preferably30 to 40 mm and the cut length to 20 to 70 mm, preferably 25 to 65 mm.

Since the solid fuel of the present invention is preferably manufacturedby the above molding method from the industrial point of view, its shapeis preferably cylindrical or prismatic, particularly preferablycylindrical. As for the size of the solid fuel, its average volume is 15to 3,500 cm³, preferably 20 to 1,000 cm³.

The apparent specific gravity of the solid fuel is 0.3 to 0.6 g/cm³,preferably 0.4 to 0.5 g/cm³.

The solid fuel has a stable calorific value of 15 to 30 MJ/kg,preferably 20 to 28 MJ/kg. Therefore, the solid fuel of the presentinvention has a highly stable calorific value and excellent formretention stability and is therefore advantageously used as a fuel forthermal power generation.

EXAMPLES

A form retention stability test was made on solid fuels obtained inExamples by the following method.

100 kg of the solid fuel was put into a metal can (drum can) having acapacity of 200 liters, the can was rolled 100 m on a flat asphalt roadfor 3 minutes, and this was repeated 5 times (a total of 1,000 m).Thereafter, the solid fuel was taken out from the metal can and theratio (%) of the solid fuel passing through a sieve having an opening of10 mm or less was taken as form retention stability.

(Evaluation Criteria)

The ratio (weight) of the solid fuel passing through a sieve having anopening of 10 mm or less was calculated and evaluated based on thefollowing criteria.

-   0 to 5% or less: satisfactory-   6 to 10% or less: acceptable-   11 to 15%: unsatisfactory

Examples 1 to 8

Cylindrical solid fuels having an extrusion diameter of about 50 mm(length of 65 mm) were obtained from the residues of plants shown inTable 1 below as raw material compositions (each composition contained80 wt % of the dried residue and 20 wt % of natural rubber) by means ofa double-screw extruder heated at 130° C. The apparent specific gravity(bulk specific gravity), calorific value and form retention stabilitytest result of each of the obtained solid fuels are shown in Table 1below.

TABLE 1 Product Bulk Type of raw specific Calorific value Form materialSize gravity Joule Calorie retention Type (80 wt % or more) mm g/cm(MJ/kg) (cal/g) stability Ex. 1 Solid Arundo donax 50 0.47 26.86 6415.4satisfactory (sample (1)) Ex. 2 Solid Leucaena 50 0.51 25.11 5997.4satisfactory (sample (2)) leucocephala Ex. 3 Solid Saccharum 50 0.4826.43 6312.7 satisfactory (sample (3)) officinarum Ex. 4 Solid Manihot50 0.52 22.10 5278.5 satisfactory (sample (4)) esculenta Ex. 5 SolidStraw 50 0.45 24.62 5880.4 satisfactory (sample (5)) Ex. 6 Solid Seaweed50 0.55 24.84 5932.9 satisfactory (sample (6)) Ex. 7 Solid Seagrass 500.51 22.89 5467.2 satisfactory (sample (7)) Ex. 8 Solid Algae 50 0.5420.22 4829.5 satisfactory (sample (8))

1. A solid fuel which comprises a composition containing 70 wt % ormore, on dry basis, of dried Arundo donax, Leucaena leucocephala,Saccharum officinarum, Manihot esculenta, straw, seaweed, seagrass oralgae and which is hot compression molded.
 2. The solid fuel accordingto claim 1, wherein the composition contains 80 wt % or more, on drybasis, of dried Arundo donax, Leucaena leucocephala, Saccharumofficinarum, Manihot esculenta, straw, seaweed, seagrass or algae. 3.The solid fuel according to claim 1, wherein the composition contains 85wt % or more, on dry basis, of dried Arundo donax, Leucaenaleucocephala, Saccharum officinarum, Manihot esculenta, straw, seaweed,seagrass or algae.
 4. The solid fuel according to claim 1 which isobtained by compression molding the composition at a temperature of 80to 150° C.
 5. The solid fuel according to claim 1, wherein thecomposition contains 80 wt % or more, on dry basis, of Arundo donax. 6.The solid fuel according to claim 1, wherein the composition contains 80wt % or more, on dry basis, of Leucaena leucocephala.
 7. The solid fuelaccording to claim 1, wherein the composition contains 80 wt % or more,on dry basis, of Saccharum officinarum.
 8. The solid fuel according toclaim 1, wherein the composition contains 80 wt % or more, on dry basis,of Manihot esculenta.
 9. The solid fuel according to claim 1, whereinthe composition contains 80 wt % or more, on dry basis, of straw. 10.The solid fuel according to claim 1, wherein the composition contains 80wt % or more, on dry basis, of seaweed.
 11. The solid fuel according toclaim 1, wherein the composition contains 80 wt % or more, on dry basis,of seagrass.
 12. The solid fuel according to claim 1, wherein thecomposition contains 80 wt % or more, on dry basis, of algae.
 13. Thesolid fuel according to claim 1 having a calorific value of 15 to 30Mj/kg.
 14. The solid fuel according to claim 1 having an average size of15 to 3,500 cm³.
 15. The solid fuel according to claim 1 having anapparent specific gravity of 0.3 to 0.6 g/cm³.
 16. The solid fuelaccording to claim 1 having a fragmentation ratio of 5 wt % or less in aform retention stability test.
 17. The solid fuel according to claim 1which is used for power generation.
 18. Use of the solid fuel of claim 1as a fuel for power generation.